350 TBI runs rough if at all

[Johninbc]

The TBI is very similar in that regard, if it sits for any amount of time or hasn't been rebuilt in a while you can get all kinds of issues with fueling. A rebuild is a good idea if it has never been done to the OP's knowledge. The TBI does have a TPS, and the expected values are given in the thread I linked. A TPS issue usually shows up as an acceleration issue though.

 

[Johninbc]

It's not a big problem to throw a rebuild gasket set at the TBI,and if not the problem it will likely reward you with better milage. Don't forget the two little black washers in the kit that you don't know what to do with.
New gas wether being used or just sitting, attacks the rubber materials in the original oem pump assemblies. The pump can still be good but there is an inlet screen, a washer that it sits on, and a short 1inch or so long rubber to couple it to the outlet. These all turn to jello. The pump outlet pressure forces a hole in the jello hose. Some gas spills out back into the tank and some travels under reduced pressure to the TBI. Gradually more spills back and less flows under any pressure to TBI until the engine runs poorly then not at all. The pump is fine, just beating it's gums. You can actually pump fuel volume out an open line but block it with your finger. A fuel pressure test is a good idea, but it's such a bitch of a time to get on those fuel connections behind the throttle body. If you do replace the pump be cognizant that it is a 13 psi pump as there are lots of higher pressure pump advertised. If you are doing your TBI make sure you cover the manifold inlets - it's not going to be fun getting that stupid screw imbeaded in my my #3 piston out, and I was extremely careful.

 

[Mungo]

I'm now ordering the CTS and TB rebuild kit, thank you for your advise, yes standing up the vehicle does it no good.

 

[Mungo]

Hi, I've got some time to get back to the 350 TBI. The battery was disconnected as it slowly drains flat otherwise (must sort that issue also), so no OBD codes available. I tried starting again, it winds over fast, fires and almost catches but dies. Using a bit of throttle doesn't help much, it runs for a couple of seconds sometimes.
After trying this a few times I checked the ODB codes again by shorting the A & B terminals on the ALDL connector but nothing (flashes 1 time then 2 times, long space, flashes 1 time then 2 times). I guess not much running time to throw up a fault code and also I'm not sure that there is much in the way of fuel DTCs. This ex-USAF truck has no emissions equipment; no EGR, no CAT and no O2 sensor.
I tried the new CTS but no change, easy check though, didn't cost much, keep for later.
I got the air cleaner off and looked down the TBI bores while my son cranked the engine over; the fuel dribbles out of both injectors onto the throttle butterflies. It seems like a lot of fuel but it is definitely not spraying, this is more like dripping out of both injectors, both the same.

I can hear the fuel pump running while the engine is being cranked. Jumping terminals A & E on the fuel pump relay connector makes the fuel pump run also and I've tried starting in it like this but no difference.


I'm guessing some potential faults could be:
a) the pump is running but not making good pressure (say 4psi)
b) there is a leak on the pressure side of the pump, within the tank (short section of rubber hose in there?)
c) fuel filter on the frame blocked (eliminated this, new filter fitted)
d) another fuel filter blocked (is there a filter at the inlet of the TB?)
e) the injector electrical pulses not good

I need to check that fuel pressure. There is a fuel pressure test kit OTC 4480 that is $100 at Summit Racing but out of stock most places. This kit has a neat adaptor that screws onto the end of the fuel filter on the chassis.

Is there another kit with this type of adaptor? Less expensive would be good. There is another type that fits in place of the fuel filter, I guess not such a bad idea as you are likely to change the filter if you're checking the pressure, but stuff in the line can then go straight to the TB.

 

[Mungo]

I have a rebuild kit for the throttle body, perhaps I should take the TB off and give it a freshen up, then I have the open end of the fuel supply to adapt onto a pressure tester.